Device for starting alternating-electric-current induction-motors.



No. 694,IO5. Patented Feb. 25

, K. A. LINOST-BOM. DEVICE FOR STARTING ALTERNATING ELECTRIC CURRENT INDUCTION MOTORS.

(Application filed Dec. 29, 1899.)

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No. 694,!05. Patented Feb 25, I902.

' K. A. LINDSTROM.

DEVICE FOR STARTING ALTE RNATING ELECTRIC CURRENT INDUCTION MOTORS.

(Application filed Dec. 29, 1899.) (No Model.) 2 sheets-sheet 2.

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- UNITE AENT FFICE.

KARL ARVID LINDSTRClM, OF 'SOMMARRO, SWEDEN, ASSIGNOR TO ALLlglANNA SVENSKA ELEKTRISKA AKTIEBOLAGET, OF WES- TERAS, SWEDEN.

DEVICE FOR STARTING ALTERNATlNG-ELECTRlC-CURRENT INDUCTION-MOTORS.

SPECIFICATION forming part of Letters Patent No. 694,105, dated February 25, 1902.

Application filed December 29, 1899. Serial No. 741,971. (No model.)

T0 on whom it may concern.-

Be it known that I, KARL ARVID LIND- sTR'CSM, a subject of the King of Sweden and Norway, and a resident of Somrnarro, Westeras, Sweden, have invented a new and useful Improvement in Devices for Starting Alternating-Electric Current Induction-Motors, of which the following is a specification, reference being had to the drawings accompanying and forming a part hereof.

This invention relates to resistances for use in starting and regulating alternating-electrio-current induction-motors or the like.

In starting an induction-motor from some current source of constant potential and fre quency two essentially different methods are available. One is to admit the current from the primary side, the secondary winding being left short-cirouited from the beginning. The other is to have an extra resistance introduced in the secondary circuit when the primary current is being switched on, which extra resistance is afterward gradually removed, according as the velocity of the motor increases. The former method is accompanied by simplicity in the construction of the motor and absence of auxiliary apparatus, but at the same time great current strength is required in starting and a small torque is obtained in proportion to the current. The latter method combines the advantage of a great torque in comparison to the current strength, but necessitates the use of a starting apparatus, which, owing to sparking or chemical influences, is subjected to considerable wear and is easily destroyed. Such a starting apparatus must also be operated either by hand or automatically by some mechanical means or other.

The object of the present invention is to obtain such a starting and regulating resistance that the same when connected in series with the secondary circuit of an inductionmotor will automatically diminish during starting, so as to cause the motor to develop a great and nearly-constant torque at all speeds without the consumption or lag of current being any considerably larger at starting than at full running speed.

The invention consists, briefly, in using an inductive resistance having a small ohmic resistance and provided with a magnetic core, the hysteresis losses of which are greatin comparison to the losses due to eddy-currents in the same.

For a two or poly phase induction-motor coupled to a current source of constant potential and frequency the following relation approximately obtains:

S x 4 T2 2 in which formula T stands for equals the torque of the motor, S equals the slip equals the secondary frequency the primary frequency I ive (inductionless) resistance of the entire circuit of the secondary winding. :1: equals the inductive resistance of the same circuit for the given frequency. If r and or vary with the secondary frequency in such a manner that 1' equals 0 multiplied by S and as equals 0 S, (c and 0 being constants,) then T T equals constant 0" equals the effectequals constant and will consequently be independent of the velocity of the motor within the limits for which the above formula applies.

The current strength traversing the secondary (as well as primary) winding of the vmotor will, as is easily seen, be constant under the same conditions and within the same limits.

The winding of a closed magnetic circuit (an iron-cored induction-coil) will form a circuit ot' the kind referred to if its ohmic resistance is small and the magnetic core of the same gives rise to great losses from hysteresis in proportion to the losses by eddy (Foucault) currents. For if such a circuit be traversed by an alternating current the potential E induced in it can be divided into two components, one, 6, representing the loss of potential due to hysteresis and in phase with the current and the other, 8 representing the self-induction and leading the current by ninety degrees. As the consumption of energy in such an iron core is in proportion to the frequency at a certain constant current strength i and a magnetism to correspond,we must have: The consumption of energy equals 6 multiplied by 2', equals constant multiplied by frequency, equals 2' multiplied by r, where r equals the effective resistance, and consequently 1' equals constant multiplied by frequency, equals 0 multiplied by S. We further have: The self-inductive potential equals 9,, equals constant multiplied by frequency, equals t' multiplied by 00, Where as equals the inductive resistance, and consequently as equals constant multiplied by frequency, equals 0 multiplied by S. Consequently if an iron-cored induction-coil having great hysteresis losses is coupled in the secondary circuit of an induction-motor the latter will have a certain torque which remains unchanged, While the velocity of the motor increases from zero to approximately synchronous running. In order that the said increase of Velocity shall take place, it is of course necessary that the torque to be overcome by the motor shall at no intermediate velocity exceed that developed by the motor at the time of starting. The smaller the ohmic resistance in the secondary circuit itself the more the velocity will approximate to synchronism, as is well known.

The lag in the secondary circuit is dependent partly on the self-induction of the secondary circuit itself and partly on the amount of external inductive resistance present. If the former is the smallest possible and the latter be reduced to a sufficient extent by suitably choosing the quality of iron and the magnetic density, the said lag (difference of phase) will be slight, and consequently the current consumed in starting by the primary winding of the motor will not materially exceed that required for the motor in its normal running at full speed and for the same torque.

The resistance may be constructed in various well-known manners and placed either outside or inside the motor in the same manner as when using the resistances hitherto known, except that step-by-step connections are avoided. For a motor having several branches or phases a resistance having the same number of branches is to be used, as will be well understood by persons skilled in the art to which this invention appertains.

In the accompanying drawings, Figure 1 shows an inductive resistance according to this invention adapted to be used with a threephase induction-motor having Y-(star) coupled circuits. Fig.2 shows a similar resistance said resistance A.

having a modified form of core. Fig. 3 shows a diagram of its coupling to the secondary circuit of the motor, and Fig. 4 shows graphically the results obtained in using such a hysteresis resistance with a fifteen-horse-power motor.

B represents the closed magnetic core of the inductive resistance A, and 1, 2, and 3 represent the star-coupled windings thereof, the free ends of which are shown coupled to a switch or switches O. Said switch is so connected to the secondary winding E of the motor D that by the manipulation of the switch the said secondary winding may either be short-circuited on itself or through the In starting the motor the resistance is coupled to the secondary winding E, and after the motor has arrived at its full speed its secondary circuit is preferably shortcircuited. The inductive resistance may of course be left connected to the secondary Winding all the time, though this is not so practical. The magnetic core B is so constructed that the losses caused by hysteresis in the same are great compared to the losses caused by eddy currents. In order to obtain great hysteresis losses in the core with small weight of the core and in consequence small lag, (shifting of phase,) I prefer to use a material, such as steel or gray cast-iron, the coefficient of hysteresis of which is great. In order to obtain small losses by eddy currents, I subdivide the core in any well-known manner, as usual for said purpose.

Having now described my invention, what I claim, and desire to secure by Letters Patent, is

1. The combination, with the secondary Winding of an alternating-electriccurrent induction-motor, of an inductive resistance having a small ohmic resistance and great losses by hysteresis compared to the losses by eddy currents, for the purpose set forth.

2. A resistance of the class described, consisting of windings of small ohmic resistance on closed magnetic cores the losses by hysteresis in which are great compared to the losses by eddy currents in the same, for the purpose set forth.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

KARL ARVID LINDSTRUM.

Witnesses:

GERDA LINDKVIST, GUs'rAF IsPliU.

ICC 

